Ensure roomId are not rendered in the UI.

Add preview to see the effect.
Use RoomAvatar data fallback everywhere, to not use roomId (`!` char) for the avatar initial, but rather `#`.

libraries/matrix/impl/src/main/kotlin/io/element/android/libraries/matrix/impl/roomlist/RoomListFilter.kt

@@ -40,7 +40,7 @@ val RoomListFilter.predicate
                 (roomSummary.details.numUnreadNotifications > 0 || roomSummary.details.isMarkedUnread)
         }
         is RoomListFilter.NormalizedMatchRoomName -> { roomSummary: RoomSummary ->
-            roomSummary is RoomSummary.Filled && roomSummary.details.name.contains(pattern, ignoreCase = true)
+            roomSummary is RoomSummary.Filled && roomSummary.details.name.orEmpty().contains(pattern, ignoreCase = true)
         }
         RoomListFilter.Invite -> { roomSummary: RoomSummary ->
             roomSummary.isInvited()

libraries/matrix/impl/src/main/kotlin/io/element/android/libraries/matrix/impl/roomlist/RoomSummaryDetailsFactory.kt

@@ -33,7 +33,7 @@ class RoomSummaryDetailsFactory(private val roomMessageFactory: RoomMessageFacto
         }
         return RoomSummaryDetails(
             roomId = RoomId(roomInfo.id),
-            name = roomInfo.name ?: roomInfo.id,
+            name = roomInfo.name,
             canonicalAlias = roomInfo.canonicalAlias?.let(::RoomAlias),
             isDirect = roomInfo.isDirect,
             avatarUrl = roomInfo.avatarUrl,